CEMENTING WITH MARINE GLUE. 207 



first be heated on the mounting-plate ; and some small cuttings of 

 marine glue are then to be placed, either upon that surface of the 

 cell which is to be attached, or upon that portion of the slide on 

 which it is to lie, the former being perhaps preferable. When 

 they begin to melt, they may be worked over the surface of attach- 

 ment by means of a needle-point ; and in this manner the melted 

 glue maybe uniformly spread, care being taken to pick out any of 

 the small gritty particles which this cement sometimes contains. 

 When the surface of attachment is thus completely covered with 

 liquefied glue, the cell is to be taken up with a pair of forceps, 

 turned over, and deposited in its proper place on the slide ; and it 

 is then to be firmly pressed down with a stick (such as the handle 

 of the needle), or with a piece of flat wood, so as to squeeze out 

 any superfluous glue from beneath. If any air-bubbles should be 

 seen between the cell and the slide, these should if possible be got 

 rid of by pressure, or by slightly moving the cell from side to side ; 

 but if their presence results, as is sometimes the case, from de- 

 ficiency of cement at that point, the cell must be lifted off again, 

 and more glue applied at the required spot. Sometimes, in spite 

 of care, the glue becomes hardened and blackened by overheating ; 

 and as it will not then stick well to the glass, it is preferable not 

 to attempt to proceed, but to lift off the cell from the slide, to let 

 it cool, and then to repeat the process. When the cementing has 

 been satisfactorily accomplished, the slides should be allowed to 

 cool gradually, in order to secure the firm adhesion of the glue ; 

 and this is readily accomplished, in the first instance, by pushing 

 each, as it is finished, towards one of the extremities of the plate, 

 which is of course cooler than the centre. If two plates are in use, 

 the heated plate may then be readily moved away upon the ring 

 which supports it, the other being brought down in its place ; and 

 as the heated plate will be some little time in cooling, the firm 

 attachment of the cells will be secured. If, on the other hand, 

 there be only a single plate, and the operator desire to proceed at 

 once in mounting more cells, the slides already completed should be 

 carefully removed from it, and laid upon a wooden surface, the 

 slow conduction of which will prevent them from cooling too fast. 

 Before they are quite cold, the superfluous glue should be scraped 

 from the glass with a small chisel or awl ; and the surface should 

 then be carefully cleansed with a solution of Potash, which may be 

 rubbed upon it with a piece of rag covering a stick shaped like a 

 chisel. The cells should next be washed with a hard brush and 

 soap and water, and may be finally cleansed by rubbing with a little 

 weak spirit and a soft cloth. In cases in which appearance is not 

 of much consequence, and especially in those in which the cell is 

 to be used for mounting large opaque objects, it is decidedly pre- 

 ferable not to scrape off the glue too closely round the edges of 

 attachment, as the ' hold ' is much firmer, and the probability of 



